The invention relates to a multistage centrifugal pump with a pump housing having an inlet and an outlet. A plurality of stage housings are arranged in the pump housing, each stage housing having an impeller and a guide vane system. The stage housings, together with a pump shaft, are designed as a withdrawable pump unit. A compensating device is arranged within the pump housing to compensate changes in axial length of the withdrawable pump unit.
U.S. Pat. No. 5,456,577 discloses a compensating device in the form of a compensator for multistage centrifugal pumps. To this end, on the last stage housing subject to flow, a wall area extending radially to the shaft is designed as a disk spring. This spring action is intended to compensate any change in length that occurs during pump operation and standby operation. This type of compensator requires very special and costly production of the last stage housing, or of the guide vane system of the last pump stage. Due to the use of only a single disk spring, there is a risk of material fatigue during prolonged operation. Furthermore, such a solution is ineffective when a pump thus equipped is subjected to an overhaul. During the overhaul work, the support surface or sealing surface of an individual stage housing is frequently reworked, which causes the entire length of a withdrawable pump unit formed of a plurality of stage housings to be shortened. As a result the force of the disk spring element of the last pump stage is negatively affected.
U.S. Pat. No. 4,098,558 discloses assembly aids for a withdrawable pump unit for the foregoing type of pump. To assemble it, the stage housing parts located on the pump shaft are biased against one another by means of the assembly aid.
An individual large disk spring designed as a separate component generates the biasing forces between the discharge-side housing cover, which seals the pump housing, and the last pump stage. After the withdrawable pump unit has been installed in the pump housing and the outer housing cover has been mounted, the assembly aids are dismantled. The disk spring then generates the necessary forces for the stage housing of the withdrawable pump unit. Such a large single disk spring is costly to produce, requires a substantial amount of work in the assembly of the interacting components, and has the disadvantages of the previously discussed solution.
The design described in U.S. Pat. No. 4,218,181 also requires special assembly means to enable a prestressed withdrawable pump unit to be inserted into the pump housing. A special type of lock effects locking between pump housing and housing cover. The individual disk spring used here is also costly to produce and involves the well-known risks regarding service life.
The object of the invention is to provide a compensation device which is easy to assemble and simple to produce, but ensures a reliable compensating effect in different operating states of a multistage centrifugal pump and assures the operability of the pump even after an overhaul. This object is achieved by the features of claim 1.
By constructing the compensating device in the form of a plurality of elastically resilient compensator modules, which are designed as multielement structural units, permits a substantially simpler adaptation of such a compensating device.
The use of a plurality of multi-element compensator modules, in which a plurality of elastically resilient compensator elements are disposed, has the advantage that smaller units are formed. This makes it possible to use commercially available compensator elements, which eliminates the costly production of specially designed compensator elements. The multi-element structure of the compensator modules provides the significant advantage that, if the pump is overhauled and the length of the withdrawable pump unit changes as a result, the change in length can be readily compensated by simply adding further compensator elements in the respective structural units. By distributing the compensator elements over a plurality of modules, the modules, depending on the design of the withdrawable pump unit, can be arranged at various locations. This permits simple adaptation of a standardized compensator module to pumps of various designs. Depending on the size of the withdrawable pump unit, which is a function of the number of stage housings used, the compensator modules can be arranged at the most suitable locations within a withdrawable pump unit.
According to one embodiment of the invention, the compensator modules are distributed over an surface area as well as arranged between a housing cover of the pump housing and a first or last stage or an impeller of the withdrawable pump unit. According to this solution, such a housing cover which seals the housing can be used for a plurality of pump housings of different lengths, so that only one housing cover is required for the housings of different pump sizes. The use of a standardized housing cover, which can be arranged on the inlet or the discharge side, or as an intermediate stage cover, easily simplifies the compensation of a change in the overall length in case of a temperature shock to which the pump is subjected.
A particularly effective design has proven to be one in which the compensator elements in the compensator modules are formed by a plurality of disk springs, which are arranged in the form of packets. In a single or multiple alternating arrangement of the compensator elements or disk springs in the corresponding compensator modules, the changes in length that occur due to the existing temperature loads can be compensated in the simplest manner.
To simplify the assembly of a pump equipped with such a compensating device, a further embodiment of the invention provides that the compensator elements, which are arranged in the form of packets, be guided in a holder and provided with load transmission means. The load transmission means serves to transfer the corresponding compensation forces to the withdrawable pump unit, or the stage housings or impellers forming the withdrawable pump unit. The compensator elements or disk springs can fit directly against one of the housing covers of the pump housing for simple support.
Guiding means hold the compensator elements arranged in the form of packets at their intended location. These means can be a housing cover, an impeller and/or a stage housing. Securing elements hold the compensator elements which are arranged in the form of packets, and/or the load transmission elements in their respective installed positions. This ensures substantially simpler handling during pump assembly. The compensator modules mounted at their intended location, e.g., a housing cover, are thus held positively in position. It has proven to be advantageous if the securing elements are positioned such that the compensating device is held in place prior to assembly of the pump housing. The necessary biasing forces are applied only when all the components are in position and the pump housing is sealed by means of the clamping bolts. This ensures a simpler design of the securing elements and reduces the risk of accidents during assembly.
Any risk of injury during dismantling of the pump due to suddenly released compensator elements can also be reduced.